Use of ultrasound in medical imaging has greatly increased during the past few decades. Currently, this method of diagnostic imaging is widespread and inexpensive; reasonable quality real-time images of internal organs can be obtained. Ultrasound imaging systems are small, mobile and have low cost. A general disadvantage of this modality in comparison with nuclear medicine and magnetic resonance imaging (MRI) techniques is its lower specificity. In many instances medical ultrasound is unable to distinguish between normal and diseased tissues.
A major improvement was achieved with the recent introduction of the ultrasound contrast materials, which could be used to aid delineation of blood/tissue boundaries and help visualize blood flow and blood supply in various organs. The most efficient ultrasound contrast materials are gas microbubbles, which are strong scatterers of ultrasound. Microbubble dispersions can be administered to the patient intravenously or by other routes. Subsequent to administration, the microbubble-containing tissues of the body are visible on the screen of the imaging system as bright areas. However, even with the use of these contrast materials, selective enhancement of certain diseased tissues for ultrasound imaging is still far from clinical application. This task of selective enhancement might be achieved with targeted ultrasound contrasts.
Targeting of various contrast agents used for other imaging modalities has been performed for decades. Small molecules, macromolecules, polymers and particles have been successfully delivered to target sites for specific enhancement of the diseased tissue images. Such imaging agents have slowly made their way into clinical practice. Targeted ultrasound contrast agents, which could selectively bind to the specific sites after in vivo administration, were postulated more than a decade ago. Still, commercially successful targeted ultrasound contrast agents have yet to be reported.
It would be beneficial to design a targetable microbubble ultrasound contrast agent that would selectively bind to the areas of interest in the body and enhance the target contrast in the ultrasound examination.